1. Field of the Invention
The invention relates to the field of turboengine rotors and more specifically to the retention of rotor blades on a rotor disk.
2. Description of the Related Art
A turboreactor having a front fan and turn spool, for example, conventionally comprises, in sequence in a downstream direction, a fan, a low-pressure compressor stage, a high-pressure compressor stage, a combustion chamber, a high-pressure turbine stage and a low-pressure turbine stage.
In the present application, the terms “upstream” and “downstream” are, by convention, defined relative to the direction of circulation of air in the turboreactor. In the same manner, in the present application, the terms “inner” and “outer” are, by convention, defined radially relative to the axis of the engine. Thus, a cylinder which extends along the axis of the engine comprises an inner face which is directed toward the axis of the engine and an outer surface opposite the inner surface thereof.
In conventional manner, with reference to FIG. 1, a low-pressure turbine stage comprises, for example, successive rotor disks 1 which each comprise axial or oblique grooves 11 in which blades 2 are engaged by means of the roots 3 thereof, the blades 2 extending radially outward relative to the axis X of the engine.
The blades 2 are radially retained in the grooves by means of the fir-tree-like roots 3 thereof which further allows a space to be created between the root 3 and the base of the groove in order to allow a circulation of air which is guided in the body of the blades in order to ventilate them. The blades 2 are retained in an axially upstream direction by means of a sealing ring 4 which comprises sealing plates, the sealing ring 4 being known to the person skilled in the art as a “labyrinth ring”.
In order to retain the blades 2 in an axially downstream position, a circumferential ring sector 5 is mounted between a recess 6 of the rotor disk 1 and a downstream hook 7 of the root 3 of the blade 2. In this manner, in the position for use, the ring sector 5 blocks the axial movement of the blade 2 in a downstream direction, the blade 2 remaining fixedly joined to the rotor disk 1.
Currently, the roots 3 of the blades 2 are of metal material. In order to reduce the mass of the engine, it is proposed that the roots 3 be formed of composite material. The current method for fixing a metal root cannot be transferred to the fixing of a root made of composite material. This is because a conventional composite material does not allow concave zones to be formed simply in the blade root. Thus, it is difficult to form a downstream hook in the blade root in order to ensure the downstream axial retention of the blade by a ring sector. Furthermore, the production of a fir-tree-like blade root from composite material is not preferred. This is because during the operation of the engine, differential expansions appear and the teeth of the fir-tree-like root are no longer in abutment in the groove of the rotor disk. The radial retention of the blade is not satisfactory.